#define _CRT_SECURE_NO_WARNINGS 1

struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2) {
    struct ListNode* head = NULL;
    struct ListNode* tail = NULL;
    head = tail = (struct ListNode*)malloc(sizeof(struct ListNode));
    while (list1 && list2)
    {
        if (list1->val > list2->val)
        {
            tail->next = list2;

            list2 = list2->next;
        }
        else
        {
            tail->next = list1;

            list1 = list1->next;
        }
        tail = tail->next;
    }
    if (list1)
    {
        tail->next = list1;
    }
    else
    {
        tail->next = list2;
    }
    struct ListNode* poi = head;
    head = head->next;
    free(poi);
    return head;
}